1. Field of the Invention
The present invention relates to a stress measurement method using X-ray diffraction. In particular, the present invention relates to a stress measurement method for a c-axis-oriented specimen of a tetragonal polycrystal.
2. Description of the Related Art
In general, a sin2 ψ method has been used wish for the stress measurement method using X-ray diffraction. The sin2 ψ method requires four conditions: (1) the crystal grain is small, (2) there is no strong preferred orientation, (3) a plane stress state is established within the depth of penetration of the X-ray, and (4) no stress gradient is present in the depth direction.
The stress measurement of a polycrystalline specimen, in which a specific crystal axis orients in a specific direction (such an orientation is referred to as a fiber texture), using the conventional sin2 ψ method does not satisfy the above-described condition (2) including no strong preferred orientation. Therefore, the stress measurement of the fiber texture specimen using the sin2 ψ method provides not a correct value but an approximate value.
With respect to such a fiber texture specimen, measurement methods more precise than the conventional sin2 ψ method have been developed. Only for a fiber texture specimen of a cubic or hexagonal polycrystal, measurement methods more precise than the conventional sin2 ψ method have been developed. For example, with respect to the cubic system, Tanaka, K., Ishihara, K. and Inoue, K., J. Soc. Mat. Sci., Japan, Vol. 45, No. 8, p. 945–950, 1996 discloses calculation formulae in a stress measurement method for the [111] fiber texture of a cubic polycrystal ([111] is perpendicular to the specimen surface). Besides, Tanaka, K., Akiniwa, Y., Ito, T. and Inoue, K., JSME International Journal, Series A, Vol. 42, No. 2, p. 224–234, 1998 discloses calculation formulae in a stress measurement method for the <111>, <100> and <110> fiber textures of a cubic polycrystal. With respect to the hexagonal system, Tanaka, K. and Akiniwa, Y., JSME International Journal, Series A, Vol. 41, No. 2, p. 287–289, 1998 discloses calculation formulae in a stress measurement method for the [001] fiber texture of a hexagonal polycrystal (only for an equi-biaxial stress state).
However, with respect to a fiber texture specimen of a tetragonal polycrystal (in this case, the c-axis of the tetragonal system is perpendicular to the specimen surface, the specimen being a c-axis-oriented specimen), no stress measurement method more precise than the conventional sin2 ψ method has been developed. The stress measurement of the c-axis-oriented specimen of the tetragonal polycrystal is strongly desired in, for example, a semiconductor industry. Since there are many c-axis-oriented specimens in tetragonal specimens such as PZT, a stress measurement method for such specimens is desired.